Number of simple graphs on n unlabeled nodes with maximum degree exactly 2.

Terms

a(0) =0a(1) =0a(2) =2a(3) =4a(4) =8a(5) =15a(6) =25a(7) =41a(8) =65a(9) =100a(10) =150a(11) =225a(12) =327a(13) =474a(14) =678a(15) =962a(16) =1348a(17) =1884a(18) =2602a(19) =3581a(20) =4889a(21) =6644a(22) =8968a(23) =12064a(24) =16124a(25) =21476a(26) =28462a(27) =37585a(28) =49407a(29) =64747